ENHANCEMENT OF BANDWIDTH AND GAIN OF A
RECTANGULAR MICROSTRIP PATCH ANTENNA
A thesis submitted in partial fulfillment of the requirements for the
degree of Bachelor of Technology
in
Electronics and Communication Engineering
By
V. Mohan Kumar (10609013)
N. Sujith (10607024)
Under the supervision of
Prof. S. K. Behera
Department of Electronics and Communication Engineering
National Institute of Technology
Rourkela
2010
Department of Electronics and Communication Engineering
National Institute of Technology, Rourkela-769008
CERTIFICATE
This is to certify that the thesis entitled, “ENHANCEMENT OF BANDWIDTH AND
GAIN OF A RECTANGULAR MICROSTRIP PATCH ANTENNA” submitted by Mr. V.
Mohan Kumar and Mr. N. Sujith in partial fulfillment of the requirements for the award of
Bachelor of Technology Degree in ELECTRONICS AND COMMUNICATION and
ELECTRONICS AND INSTRUMENTATION respectively at the National Institute of
Technology, Rourkela is an authentic work carried out by them under my supervision and
guidance. To the best of my knowledge, the matter embodied in the thesis has not been submitted
to any other University/ Institute for the award of any degree or diploma.
Date: Dr. S. K. BEHERA,
Associate Professor.
ACKNOWLEDGEMENTS
We express my sincere gratitude and indebtedness to the thesis guide Prof. S. K. Behera,
for his initiative in this field of research, for his valuable guidance, encouragement and affection
for the successful completion of this work. His sincere sympathy and kind attitude always
encouraged us to carry out the present work firmly. We express our thankfulness to Prof. S. K.
Patra, Head of the Department of Electronics and Communication Engineering, NIT, Rourkela,
for providing us with best facilities in the Department and his timely suggestions. We would also
like to thank Natarajamani S for his guidance and suggestions in our work.
Last but not least we would like to thank all my friends and well wishers who were
involved directly or indirectly in successful completion of the present work.
V. Mohan Kumar
N. Sujith
ABSTRACT
In this project, method of moments based IE3D software is used to design a Microstrip
Patch Antenna with enhanced gain. The aim of the project is to design a rectangular Microstrip
Patch Antenna with enhanced gain and bandwidth and study the effect of antenna dimensions
Length (L), Width (W) and substrate parameters relative Dielectric constant (ε r), substrate
thickness on antenna gain and bandwidth. The conducting patch can take any shape but
rectangular and circular configurations are the most commonly used configuration. Other
configurations are complex to analyze and require heavy numerical computations. The length of
the antenna is nearly half wavelength in the dielectric, it is a very critical parameter, which
governs the resonant frequency of the antenna. In view of design, selection of the patch width
and length are the major parameters along with the feed line depth. Desired Patch antenna design
is simulated by using IE3D simulator. And Patch antenna is realized as per design requirements.
A wideband phi-shape microstrip patch antenna has been designed. The return loss is below −10
dB from 4.45 GHz to 7.4 GHz except at 5.1GHz with a bandwidth of 48%.The antenna is thin
and compact which makes it easily portable. A maximum gain of 8.77dB achieved at 4.7 GHz
frequency. The VSWR parameter was found to be less than 2 within the operating frequenc y
range. It can be used for wireless Local Area Network application in the frequency range 5.2 to
5.8 GHz.
CONTENTS
Nomenclature Page No
List of Figures i
List of Tables ii
Chapter 1 Introduction 01
1.1 Objective of Project 01
1.2 Antenna characteristics 01
1.3 Microstrip Patch Antenna 02
1.4 Advantages and Disadvantages 03
1.5 Different Feed Techniques 05
1.6 Transmission Line Model 06
1.7 Organization of the Thesis 10
Chapter 2 Properties of a Basic Microstrip Patch 11
2.1 Dimensions 13
2.2 Impedance matching 14
2.3 Radiation pattern 15
2.4 Antenna Gain 17
2.5 Methods To Enhance Gain In Microstrip Patch Antenna 18
2.6 Polarization 18
2.7 Bandwidth 19
Chapter 3 Study of U-slotted and E-shaped Microstrip 22 Patch Antenna
3.1 Introduction 22
3.2 Design Specifications for U-slotted rectangular patch 22
3.3 Simulation Results in IE3D for U-slotted patch 24
3.4 Parametric Study of U-Slotted rectangular patch 25
3.5 Design of E-shaped patch with dual substrate 27
3.6 E-shaped patch with coaxial probe feeding 29
3.7 Simulated Results and Discussion 30
Chapter 4 Design of Phi shaped Microstrip patch antenna 35
in IE3D
4.1 Introduction to phi-shaped microstrip patch antenna 35
4.2 Design Specifications 35
4.3 Simulated results and Discussion 37
4.3.1 Enhancement of Bandwidth and gain by varying 37
Ws, Ls, R and Feed position
4.3.2 Return Loss and VSWR Display 40
4.3.3 Z-Parameter Display and Antenna Gain 41
4.3.4 Radiation Pattern 42
Chapter 5 Conclusion and Future Prospects 43
LIST OF FIGURES: PAGE NO
Figure 1.1: Microstrip patch antenna 2
Figure 1.2: Comparison of different feed techniques 5
Figure 1.3: (a) Microstrip Line (b) Electric Field Lines 6
Figure 1.4: Microstrip Patch Antenna 8
Figure 1.5: (a) Top View of Antenna (b) Side View of Antenna 8
Figure 2.1: Basic Microstrip patch antenna with probe 11
feeding
Figure 2.2: Current distribution on the patch surface 14
Figure 2.3: Voltage (U), Current (I), Impedance (Z) 14
distribution along the patch’s resonant length
Figure 2.4: Typical radiation pattern of a square patch 16
Figure 2.5: VSWR bandwidth Calculation 20
Figure 3.1: Designed Patch 24
Figure 3.2: S Parameter display 24
Figure 3.3: S-Parameter display with enhanced 26
bandwidth
Figure 3.4: Equivalent circuits of (a) Rectangular 27
Patch and (b) E-shaped Microstrip Antennas
Figure 3.5: (a) E-shaped patch (b) Substrate Dimensions 29
Figure 3.6: S-Parameter Results compared by varying 30
slot width w1
Figure 3.7: S-Parameter Results compared by varying 31
slot length l
Figure 3.8: S-Parameter Results compared by varying 31
slot width w2
Figure 3.9: Simulated Return Loss Curve 32
Figure 3.10: Simulated VSWR Curve 32
Figure 3.11: Simulated Z-parameter 33
i
Figure 3.12: Gain Vs Frequency 33
Figure 3.13: E and H plane Radiation Pattern 34
Figure 4.1: Phi shaped patch dimensions 37
Figure 4.2: Phi shaped patch substrate specifications 37
Figure 4.3: Comparing the results obtained by varying 38
Width of the Slot (Ws)
Figure 4.4: Comparing the results obtained by varying 38
Length of the Slot (Ls)
Figure 4.5: Comparing the results obtained by varying 39
Feed point position
Figure 4.6: Comparing the results obtained by varying 39
Radius of the Probe feed
Figure 4.7: Simulated Return Loss Curve 40
Figure 4.8: Simulated VSWR Curve 40
Figure 4.9: Simulated Z-parameter 41
Figure 4.10: Gain Vs Frequency 41
Figure 4.11: E and H plane Radiation Pattern 42
LIST OF TABLES: PAGE NO
Table 1.1: Comparison of different feed techniques 6
Table 3.1: S-parameter Study of U-Slotted rectangular 25
patch by varying probe feed point position
ii
1
CHAPTER 1
INTRODUCTION
Communication between humans was first by sound through voice. With the desire for
slightly more distance communication came, devices such as drums, then, visual methods such as
signal flags and smoke signals were used. These optical communication devices, of course,
utilized the light portion of the electromagnetic spectrum. It has been only very recent in human
history that the electromagnetic spectrum, outside the visible region, has been employed for
communication, through the use of radio. One of humankind’s greatest natural resources is the
electromagnetic spectrum and the antenna has been instrumental in harnessing this resource.
1.1 Objective of Project
Microstrip patch antenna is used to send onboard parameters of article to the ground
while under operating conditions. The aim of the thesis is to design rectangular Microstrip Patch
Antenna with enhanced gain and bandwidth and study the effect of antenna dimensions Length
(L), Width (W) and substrate parameters relative Dielectric constant (εr), substrate thickness (t)
on the Radiation parameters of Bandwidth and Beam-width.
1.2 Antenna Characteristics
An antenna is a device that is made to efficiently radiate and receive radiated
electromagnetic waves. There are several important antenna characteristics that should be
considered when choosing an antenna for your application as follows:
• Antenna radiation patterns
• Power Gain
2
• Directivity
• Polarization
1.3 Microstrip Patch Antenna
In its basic form, a Microstrip Patch antenna consists of a radiating patch on one side of a
dielectric substrate which has a ground plane on the other side as shown in Figure.1.1
Figure 1.1: Microstrip patch antenna
The patch is normally made of conducting material such as copper or gold and can take
any possible shape. The radiating patch and the feed lines are usually photo etched on the
dielectric substrate.
In order to simplify analysis and performance estimation, generally square, rectangular,
circular, triangular, and elliptical or some other common shape patches are used for designing a
microstrip antenna.
For a rectangular patch, the length L of the patch is usually 0.3333λo< L < 0.5 λo, where
λo is the free-space wavelength. The patch is selected to be very thin such that t << λo (where t is
3
the patch thickness). The height h of the dielectric substrate is usually 0.003 λo≤h≤0.05 λo. The
dielectric constant of the substrate (εr) is typically in the range 2.2 ≤ εr≤ 12.
Microstrip patch antennas radiate primarily because of the fringing fields between the
patch edge and the ground plane. For good performance of antenna, a thick dielectric substrate
having a low dielectric constant is necessary since it provides larger bandwidth, better radiation
and better efficiency. However, such a typical configuration leads to a larger antenna size. In
order to reduce the size of the Microstrip patch antenna, substrates with higher dielectric
constants must be used which are less efficient and result in narrow bandwidth. Hence a trade-off
must be realized between the antenna performance and antenna dimensions.
1.4 Advantages and Disadvantages
Microstrip patch antennas are mostly used in wireless applications due to their low-
profile structure. Therefore they are extremely compatible for embedded antennas in handheld
wireless devices such as cellular phones, pagers etc...
Some of the principal advantages are given below:
• Light weight and less volume.
• Low fabrication cost, therefore can be manufactured in large quantities.
• Supports both, linear as well as circular polarization.
• Low profile planar configuration which can be easily made conformal to host surface.
• Can be easily integrated with microwave integrated circuits (MICs).
• Capable of dual and triple frequency operations.
• Mechanically robust when mounted on rough surfaces.
4
Microstrip patch antennas suffer from more drawbacks as compared to conventional
antennas.
Some of their major disadvantages are given below:
• Narrow bandwidth
• Low efficiency
• Low Gain
• Low power handling capacity.
• Surface wave excitation
• Extraneous radiation from feeds and junctions
• Poor end fire radiator except tapered slot antennas
Microstrip patch antennas have a very high antenna quality factor (Q). It represents the
losses associated with the antenna where a large Q leads to narrow bandwidth and low
efficiency.
Q can be decreased by increasing the thickness of the dielectric substrate. But as the
thickness increases, an increasing fraction of the total power delivered by the source goes into a
surface wave. This surface wave contribution can be counted as an unwanted power loss since it
is ultimately scattered at the dielectric bends and causes degradation of the antenna
characteristics.
5
1.5 Different Feed Techniques
Feed Techniques
Microstrip patch antennas can be fed by a variety of methods. These methods can be
classified into two categories- contacting and non-contacting. In the contacting method, the RF
power is fed directly to the radiating patch using a connecting element such as a microstrip line.
In the non-contacting scheme, electromagnetic field coupling is done to transfer power between
the microstrip line and the radiating patch.
Different Types of Feeding Techniques
Figure 1.2: Comparison of different feed techniques
6
Table 1.1: Comparison of different feed techniques
1.6 Transmission Line Model
This model represents the microstrip antenna by two slots of width W and height h,
separated by a transmission line of length L. The microstrip is essentially a non-homogeneous
line of two dielectrics, normally the substrate and air.
(a) (b)
Figure 1.3(a) Microstrip Line (b) Electric Field Lines
7
Hence, as shown in Figure.1.3 (b), most of the electric field lines lies in the substrate and
parts of some lines are in air. As a result, this transmission line do not support pure transverse-
electromagnetic mode of transmission, since the phase velocities would be different in the air
and the substrate. Instead, the dominant mode of propagation would be the quasi-TEM mode.
Hence, an effective dielectric constant (εreff) must be obtained in order to account for the
fringing and the wave propagation in the line. The value of εreff is little less then εr because the
fringing fields around the edge of the patch are not confined in the dielectric substrate but are
also spread in the air as shown in Figure above. The expression for εreff can be given as:
Where εreff = Effective dielectric constant
εr = Dielectric constant of substrate
H = Height of dielectric substrate
W = Width of the patch
Consider Figure 1.4, which shows a rectangular microstrip patch antenna of length L,
width W lying on a substrate of height h. The co-ordinate axis is selected in such a way that the
length is along the x axis direction, width is along the y axis direction and the height is along the
z axis direction.
8
Figure 1.4: Microstrip Patch Antenna
In order to operate in the TM10 mode, the length of the patch must be slightly less than
λ/2 where λ is the wavelength in the dielectric medium and is equal to λo/√εreff where λo is the
free space wavelength. The TM10 mode implies that the field varies one λ/2 cycle along the
length, and there is no difference along the width of the patch. In the Figure 1.5, the microstrip
patch antenna is shown by two slots and separated by a transmission line of length L and open
circuited at both the ends. Along the width of the patch, the voltage is maximum and current is
minimum due to the open ends. The fields at the edges can be resolved into normal and
tangential components with respect to the ground plane.
(a) (b)
Figure 1.5 :( a) Top View of Antenna (b) Side View of Antenna
9
It is shown in Figure 1.5.b that the normal components of the electric field at the two
edges along the width are in opposite directions and thus out of phase since the patch is λ/2 long
and hence they nullify each other in the broadside direction. The tangential components which
are in phase, means that the resulting fields combine to give maximum radiated field normal
to the surface of the structure. Hence the edges along the width can be represented as two
radiating slots, which are λ/2 apart and excited in phase and radiating in the half space above the
ground plane.
The fringing fields along the width can be modeled as radiating slots and electrically the
patch of the microstrip antenna looks greater than its physical dimensions. The dimensions of the
patch along its length have now been extended on each end by a distance ΔL, which is given
empirically as:
The effective length of the patch Leff now becomes:
For a given resonance frequency fo, the effective length is given by as:
10
For a rectangular Microstrip patch antenna, the resonance frequency for any TMmn mode is given
by as:
Where m and n are modes along L and W respectively.
For efficient radiation, the width W is given as;
1.7 Organization of the Thesis
An introduction to microstrip antennas was given in Chapter I. Apart from the advantages
and disadvantages, the various feeding techniques and models of analysis were listed.
Chapter II deals with the Basic parameters that are considered while designing of
Microstrip patch antenna. The theory of radiation, various parameters and design aspects were
discussed.
Chapter III provides the design and parametric study of U-slotted and E-shaped
Microstrip patch antenna with enhanced gain and bandwidth.
Chapter IV provides the design and development of phi shaped microstrip antenna with
more enhanced gain and bandwidth compared to previous U-slotted and E-shape.
Chapter V gives the Conclusion to this project and suggests the future prospects.
11
CHAPTER 2
Properties of a Basic Microstrip Patch
A microstrip or patch antenna is a low profile antenna that has a number of advantages
over other antennas it is lightweight, low cost, and easy to integrate with accompanying
electronics. While the antenna can be 3D in structure (wrapped around an object, for example),
the elements are usually flat; hence their other name, planar antennas. Note that a planar antenna
is not always a patch antenna.
The figure 2.1 shows a patch antenna in its basic form: a flat plate on a ground plane. The
center conductor of a coax serves as the feed probe to couple electromagnetic energy in and/or
out of the patch. The electric field distribution of a rectangular patch in its fundamental mode is
also shown
Figure 2.1: Basic Microstrip patch antenna with probe feeding
12
The electric field is zero at the center of the patch, maximum (positive) at one side, and
minimum (negative) on the opposite side. It should be mentioned that the minimum and
maximum continuously change side according to the instantaneous phase of the applied signal.
The electric field does not stop abruptly at the patch's periphery as in a cavity rather, the fields
extend the outer periphery to some degree. These field extensions are known as fringing fields
and cause the patch to radiate. Some popular analytic modeling techniques for patch antennas are
based on this leaky cavity concept. Therefore, the fundamental mode of a rectangular patch is
often denoted using cavity theory as the TM10 mode.
Since this notation frequently causes confusion, we will briefly explain it. TM stands for
transversal magnetic field distribution. This means that only three field components are
considered instead of six. The field components of interest are: the electric field in the z
direction, and the magnetic field components in x and y direction using a Cartesian coordinate
system, where the x and y axes are parallel with the ground plane and the z axis is perpendicular.
In general, the modes are designated as TMnmz. The z value is mostly omitted since the
electric field variation is considered negligible in the z axis.
Hence TMnm remains with n and m the field variations in x and y direction. The field
variation in the y direction (impedance width direction) is negligible; thus m is 0. And the field
has one minimum to maximum variation in the x direction (resonance length direction); thus n is
1 in the case of the fundamental. Hence the notation TM10.
13
2.1 Dimensions
The resonant length determines the resonant frequency and is about l/2 for a rectangular
patch excited in its fundamental mode. The patch is, in fact, electrically a bit larger than its
physical dimensions due to the fringing fields. The deviation between electrical and physical size
is mainly dependent on the PC board thickness and dielectric constant.
A better approximation for the resonant length is:
This formula includes a first order correction for the edge extension due to the fringing
fields, with:
· L = resonant length
· λd = wavelength in PC board
· λo = wavelength in free space
· εr = dielectric constant of the PC board material
Other parameters that will influence the resonant frequency:
· Ground plane size
· Metal (copper) thickness
· Patch (impedance) width
14
2.2 Impedance Matching
Looking at the current (magnetic field) and voltage (electrical field) variation along the
patch, the current is maximal at the center and minimal near the left and right edges, while the
electrical field is zero in the center and maximal near the left and minimal near the right edges.
The figures below clarify these quantities.
Figure 2.2: Current distribution on the patch surface
Figure 2.3: Voltage (U), Current (I), Impedance (Z) distribution along the patch’s resonant length
15
From the magnitude of the current and the voltage, we can conclude the impedance is
minimum (theoretically zero W) in the middle of the patch and maximum (typically around 200
W, but depending on the Q of the leaky cavity) near the edges. Put differently, there is a point
where the impedance is 50 W somewhere along the "resonant length" (x) axis of the element.
2.3 Radiation Pattern
The patch's radiation at the fringing fields results in a certain farfield radiation pattern.
This radiation pattern shows that the antenna radiates more power in a certain direction than
another direction. The antenna is said to have certain directivity. This is commonly expressed in
dB.
An estimation of the expected directivity of a patch can be derived with ease. The
fringing fields at the radiating edges can be viewed as two radiating slots placed above a ground
plane. Assuming all radiation occurs in one half of the hemisphere, this results in a 3 dB
directivity. This case is often described as a perfect front to back ratio; all radiation towards the
front and no radiation towards the back. This front to back ratio is highly dependent on ground
plane size and shape in practical cases. Another 3 dB can be added since there are 2 slots. The
slots are typically taken to have a length equal to the impedance width (length according to the y
axis) of the patch and a width equal to the substrate height. Such a slot typically has a gain of
about 2 to 3 dB .This results in a total gain of 8 to 9 dB.
The rectangular patch excited in its fundamental mode has a maximum directivity in the
direction perpendicular to the patch (broadside). The directivity decreases when moving away
from broadside towards lower elevations. The 3 dB beamwidth (or angular width) is twice the
angle with respect to the angle of the maximum directivity, where this directivity has rolled off 3
16
dB with respect to the maximum directivity. An example of a radiation pattern can be found
below.
Figure 2.4: Typical rad iation pattern of a square patch
So far, the directivity has been defined with respect to an isotropic source and hence has
the unit dBi. An isotropic source radiates an equal amount of power in every direction. Quite
often, the antenna directivity is specified with respect to the directivity of a dipole. The
directivity of a dipole is 2.15 dBi with respect to an isotropic source. The directivity expressed
with respect to the directivity of a dipole has dBd as its unit.
17
2.4 Antenna Gain
Antenna gain relates the intensity of an antenna in a given direction to the intensity that
would be produced by a hypothetical ideal antenna that radiates equally in all directions or
isotropically and has no losses. Since the radiation intensity from a lossless isotropic antenna
equals the power into the antenna divided by a solid angle of 4π steradians, we can write the
following equation:
The gain of a rectangular microstrip patch antenna with air dielectric can be very roughly
estimated as follows. Since the length of the patch, half a wavelength, is about the same as the
length of a resonant dipole, we get about 2 dB of gain from the directivity relative to the vertical
axis of the patch. If the patch is square, the pattern in the horizontal plane will be directional,
somewhat as if the patch were a pair of dipoles separated by a half-wave; this counts for about
another 2-3 dB. Finally, the addition of the ground plane cuts off most or all radiation behind the
antenna, reducing the power averaged over all directions by a factor of 2 (and thus increasing the
gain by 3 dB). Adding this all up, we get about 7-9 dB for a square patch, in good agreement
with more sophisticated approaches.
18
2.5 Methods to Enhance Gain In Microstrip Patch Antenna
Most compact microstrip antenna designs show decreased antenna gain owing to the
antenna size reduction. To overcome this disadvantage and obtain an enhanced antenna gain,
several designs for gain-enhanced compact microstrip antennas with the loading of a high-
permittivity dielectric superstrate or the inclusion of an amplifier-type active circuitry have been
demonstrated.
Use of a high-permittivity superstrate loading technique gives an increase in antenna gain
of about 10 dBi with a smaller radiating patch.
An amplifier-type active microstrip antenna as a transmitting antenna with enhanced gain
and bandwidth has also been implemented.
2.6 Polarization
The plane wherein the electric field varies is also known as the polarization plane. The
basic patch covered until now is linearly polarized since the electric field only varies in one
direction. This polarization can be either vertical or horizontal depending on the orientation of
the patch. A transmit antenna needs a receiving antenna with the same polarization for optimum
operation. The patch mentioned yields horizontal polarization, as shown. When the antenna is
rotated 90°, the current flows in the vertical plane, and is then vertically polarized.
A large number of applications, including satellite communication, have trouble with
linear polarization because the orientation of the antennas is variable or unknown. Luckily, there
is another kind of polarization circular polarization. In a circular polarized antenna, the electric
field varies in two orthogonal planes (x and y direction) with the same magnitude and a 90°
19
phase difference. The result is the simultaneous excitation of two modes, i.e. the TM10 mode
(mode in the x direction) and the TM01 (mode in the y direction). One of the modes is excited
with a 90° phase delay with respect to the other mode. A circular polarized antenna can eithe r be
righthand circular polarized (RHCP) or lefthand circular polarized (LHCP). The antenna is
RHCP when the phases are 0° and 90° for the antenna in the figure below when it radiates
towards the reader, and it is LHCP when the phases are 0° and 90°.
2.7 Bandwidth
Another important parameter of any antenna is the bandwidth it covers. Only impedance
bandwidth is specified most of the time. However, it is important to realize that several
definitions of bandwidth exist impedance bandwidth, directivity bandwidth, polarization
bandwidth, and efficiency bandwidth. Directivity and efficiency are often combined as gain
bandwidth.
Impedance bandwidth/return loss bandwidth
This is the frequency range wherein the structure has a usable bandwidth compared to a
certain impedance, usually 50 Ω. The impedance bandwidth depends on a large number of
parameters related to the patch antenna element itself (e.g., quality factor) and the type of feed
used. The plot below shows the return loss of a patch antenna and indicates the return loss
bandwidth at the desired S11/VSWR (S11 wanted/VSWR wanted). The bandwidth is typically
limited to a few percent. This is the major disadvantage of basic patch antennas.
20
Figure 2.5: VSWR bandwidth Calculat ion
Important note: Different definitions of impedance bandwidth are used, such as:
VSWR = 2:1 and other values, S11 values other than –10 dB, the maximum real
impedance divided by the square root of two [Z(Re)/√2, bandwidth], etc. This tends to turn
selecting the right antenna for a specific application into quite a burden.
Directivity/gain bandwidth
This is the frequency range wherein the antenna meets a certain directivity/gain
requirement (e.g., 1 dB gain flatness).
Efficiency bandwidth
This is the frequency range wherein the antenna has reasonable (application dependent)
radiation/total efficiency.
21
Polarization bandwidth
This is the frequency range wherein the antenna maintains its polarization.
Axial ratio bandwidth
This bandwidth is related to the polarization bandwidth and this number expresses the
quality of the circular polarization of an antenna.
22
CHAPTER 3
Study of U-slotted and E-shaped Microstrip Patch Antenna
3.1 Introduction
In this chapter, the design parameters and results for a U-slotted and E-shaped rectangular
microstrip patch antenna in IE3D software is explained and the results obtained from the
simulations are demonstrated. The microstrip patch design is achieved by using probe feed
technique. These patches were studied because they offer high bandwidth and gain.
For conventional probe-fed microstrip antennas with a thick substrate, the major problem
associated with impedance matching is the large probe reactance owing to the required long
probe pin in the thick substrate layer. To solve this problem, a variety of designs with modified
probe feeds have been reported. One design method is to cut an U slot in rectangular patch [3].
The radiating patch can be very high above the ground plane for this design and a long probe pin
is not required. This behavior makes good impedance matching over a wide bandwidth.
3.2 Design Specifications for U-slotted rectangular patch
The essential parameters for the design of a rectangular microstrip Patch Antenna are:
•Length (L): The two sides are selected to be of equal length and is 36 mm each.
•Width (W): The two sides are selected to be of equal length and is 26 mm each.
•Frequency of operation (fo): The resonant frequency of the antenna must be selected
appropriately. The resonant frequency selected for our design is 4.5 GHz.
23
•Dielectric constant of the substrate (εr): The dielectric material selected for our design has a
dielectric constant of 1.03. A substrate with a high dielectric constant has been selected since it
reduces the dimensions of the antenna.
•Height of dielectric substrate (h): For the microstrip patch antenna to be used in cellular phones,
it is essential that the antenna is not bulky. Hence, the height of the dielectric substrate is 5mm
•Slot Length along the X axis (lx): The length of slot along the X axis was adjusted to be 12 mm
in order to obtain better results.
•Slot Length along the Y axis (ly): The length of both slots along the Y axis was adjusted to be
20 mm in order to obtain better results.
•Slot Width (w): The width of all the four slits was selected to be 2 mm.
Hence, the essential parameters for the design are:
• L = 36mm
• W = 26mm
• lx = 12mm
• ly = 20 mm
• w = 2mm
• fo = 45 GHz
• εr = 1.03
• h = 5 mm
24
3.3 Simulation Results in IE3D for U-slotted patch
Designed Patch
Figure 3.1: Designed Patch
S Parameter Display and Bandwidth calculation:
Figure 3.2: S Parameter display
25
The simulation is done by varying feeding positions and s-parameter is studied for each
simulation and tabulated by taking each case. Thus the enhanced bandwidth of U-Slotted
rectangular microstrip patch is obtained as 17.49% at probe feed position (0,-1).
3.4 Parametric Study of U-Slotted rectangular patch
Feed Point
Position (mm,mm)
FREQUEBCY(F1)
(GHz)
FREQUENCY(F2)
(GHz)
Bandwidth(%)
(2,0) 4.41 4.92 10.93%
(-2,0) 4.41 4.92 10.93%
(0,-2) 4.49 5.35 17.47%
(0,-3) 4.39 4.94 11.78%
(0,-1) 4.33 5.16 17.49% *
(0,-0.5) 4.34 5.06 15.31%
(2,-2) 4.51 5.31 16.29%
(-2,-2) 4.50 5.32 16.7%
TABLE 3.1: S-parameter Study of U-Slotted rectangular patch by varying probe feed point position
26
As you can see in Table 3.1, there is no regular pattern of increment of bandwidth by varying
feed position in one direction or the other. The s-parameter variation is studied at different feed
positions in all directions all over the microstrip patch. The maximum bandwidth obtained in the
above table is the enhanced bandwidth of the U-slotted microstrip patch antenna.
FIGURE 3.3: S-Parameter d isplay with enhanced bandwidth
BANDWIDTH CALCULATION:
The bandwidth calculation at feed position (0,-1), we got maximum bandwidth. From the
figure 3.3, frequency f1 is taken as 4.33GHz and f2 is taken as 5.16GHz. Therefore the bandwidth
is obtained after doing calculation as shown in figure 3.1 as 17.49%.
27
3.5 Design of E-shaped patch with dual substrate
The E-shaped patch [2] [8] is formed by inserting a pair of wide slits at the boundary of a
microstrip patch.
Figure 3.4: Equivalent circuits of (a) Rectangular Patch and (b) E-shaped Microstrip Antennas.
A common rectangular patch antenna can be represented by means of the equivalent
circuit of Fig.(a). The resonant frequency is determined by L1C1. At the resonant frequency, the
impedance of the series LC circuit is zero, and the antenna input impedance is given by
resistance R. By varying the feed location, the value of resistance R may be controlled such that
it matches the characteristic impedance of the coaxial feed. When a pair of slots is incorporated,
the equivalent circuit can be modified into the form as shown in Fig.(b).
28
The second resonant frequency is determined by L2C2. Analysis of the circuit network
shows that the antenna input impedance is given by
The imaginary part of the input impedance is zero at the two series resonant frequencies
determined by L1C1 and L2C2, respectively. Of course, this is by no mean the exact model of
the E-shaped antenna because the equation shows that there is a parallel-resonant mode between
the two series-resonant frequencies. Nevertheless, it serves to explain the operating principle of
the antenna design. If the two series resonant frequencies are too far apart, the reactance of the
antenna at the midband frequency may be too high and the reflection coefficient at the antenna
input may be unsatisfactory. If the two series-resonant frequencies are set too near to each other,
the parallel-resonant mode may affect the overall frequency response and the reflection
coefficient near each of the series-resonant frequencies may be degraded. The question now is:
how would the slot length, slot width, slot position and the length of center arm affect the values
of L2 and C2 .This patch shape has shown to enhance gain as well as bandwidth of microstrip
patch antenna.
The need to use dual substrate
In order to further increase the bandwidth a foam material with very high thickness is
used as a substrate. In order for the structure to be practically implementable it is placed below a
substrate with 2.2 dielectric constant. The thickness of this substrate is very low to reduce
dielectric losses.
29
3.6 E-shaped patch with coaxial probe feeding
(a)
(b)
Figure.3.5:(a) E-shaped patch (b) Substrate Dimensions
The geometry of the proposed antenna is shown in fig. (a). A rectangular patch of
dimensions L x W separated from the ground plane using two substrates 1) a foam substrate (εr1)
of thickness h1 and the other 2) substrate(εr2) of thickness h2. The E-shape is located in the
center of the patch. The location of the slots on the patch can be specified by parameter W2. The
width and length of the slots are denoted by W1 and l. The rectangular patch is fed using 50Ω
coaxial probe with inner diameter of 0.65mm.
30
3.7 SIMULATED RESULTS AND DISCUSSION
In order to evaluate the performance of the proposed antenna, the antenna is simulated
through the simulation tool IE3DTM. The analysis of the antenna for different physical parameter
values has been done by varying one of them and keeping others as constant. It is carried out
here to study the flexibility in designing this of single layer patch antenna.
Parametric Study of E-patch by varying w1, w2 and l
Figure 3.6: S-Parameter Results compared by varying slot width w1
From the figure 3.6, we find that the S-Parameter bandwidth is maximum for w1=2mm
which is represented by continuous line. For other values of w1 the resonant frequency move
closer towards each other reducing the overall bandwidth.
31
Figure 3.7: S-Parameter Results compared by varying slot length l
From the figure 3.7, we find that the S-Parameter bandwidth is maximum for l = 18mm
which is represented by continuous line.
Figure 3.8: S-Parameter Results compared by varying slot width w2
32
From the figure 3.8, we find that the S-Parameter bandwidth is maximum for w2=12mm
which is represented by continuous line. The S-Parameter is less than -10dB in the frequency
range of 3.99 GHz to 5.17 GHz for the best result.
Best results were obtained for the following values of W1, W2, l and dp.
L =18mm
w1 =2mm
w2 =5mm
dp =6mm
Figure 3.9: Simulated Return Loss curve Figure 3.10: Simulated VSW R Curve
The simulated return loss value was found to be below -10dB within the frequency range
of 3.99 GHz and 5.17 GHz. The value of VSWR was also found to be within 1 and 2 in this
range. A bandwidth of 25.7% was achieved.
33
Figure 3.11: Simulated Z-parameter
Figure 3.12: Gain Vs Frequency
A maximum gain 8.8 dBi was attained at the frequency of 4.50 GHz. The gain was found
to be above 6 dBi in the entire bandwidth region. The Z-parameter was also within the
acceptable range.
34
(a) E plane(x-z)
(b)H plane(y-z)
Figure 3.13: E and H plane Radiation Pattern
Good broadside radiation patterns are observed. However, relatively large cross-
polarization radiation in the H-plane pattern is also seen, which is a common characteristic of
this kind of probe-fed microstrip antenna with a thick air substrate.
35
Chapter 4
Design of Phi shaped Microstrip patch antenna in IE3D
4.1 INTRODUCTION
Both E shape and U slot loaded single layer rectangular microstrip patch antennas have
shown the potential to give around 15-25% 2:1 VSWR impedance bandwidth on electrical thick
substrate materials. In this chapter the phi-shaped [1] microstrip patch antenna with dual
substrate is designed. It provides a much wider bandwidth than that of E-shaped patch [2].This
increased bandwidth is attributed to improved control of the current distribution on the patch by
the removal of bottom side conductors resulting in a tail part.
4.2 Design Specifications for phi-shaped rectangular patch
The essential parameters for the design of a rectangular microstrip Patch Antenna are:
•Length (L): The two sides are selected to be of equal length and is 48.5 mm each.
•Width (W): The two sides are selected to be of equal length and is 26 mm each.
•Dielectric constant of the substrates (εr): Two dielectric substrates were used to enhance
bandwidth. The first one is foam substrate with dielectric constant 1.06 and height 6mm. The
second substrate is microwave substrate with dielectric constant 2.2 and height 0.127mm.
•Slot Length along the X axis (Ws): The length of both slots along the X axis was adjusted to be
6 mm in order to obtain better results.
•Slot width along the Y axis (Ls): The width of both slots along the Y axis was adjusted to be 19
mm in order to obtain better results.
36
•Slot Width (w): The width of both the slots at the tail part was adjusted to be 6mm to obtain
better results.
Slot Width (l): The length of both the slots at the tail part was adjusted to be 23mm to obtain
better results.
Feed point position: The feed point position was adjusted to (0.6.7) to obtain better results.
Hence, the essential parameters for the design are:
• L = 48.5mm
• W = 26mm
• Ws = 6mm
• Ls = 19mm
• w = 6mm
l =23mm
• εr1 = 2.2, h1=0.127mm
• εr2 = 1.06, h2=6mm
• Feed point position (0, 6.7)
37
Figure 4.1: Ph i shaped patch dimensions
Figure 4.2: Ph i shaped patch substrate specifications
4.3 SIMULATED RESULTS AND DISCUSSION
In order to evaluate the performance of the proposed antenna, the antenna is simulated
through the simulation tool IE3D. The analysis of the antenna for different physical parameter
values has been done by varying one of them and keeping others as constant. It is carried out
here to study the flexibility in designing this of single layer patch antenna.
4.3.1 Enhancement of Bandwidth and gain by varying Ws, Ls, R and Feed position
By varying these width of the slot, length of the slot, radius of probe feed, and probe feed
position the s-parameter variation is studied and bandwidth is enhanced for the phi-shaped
microstrip patch.
38
Figure 4.3: Comparing the results obtained by varying Width of the Slot(Ws).
As you can see in figure 4.3, increase in slot width increases the central resonant
frequency and for Ws=6mm we got maximum bandwidth which is represented by continuous
line.
Figure 4.4: Comparing the results obtained by varying Length of the Slot(Ls).
2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
5
Re
turn
lo
ss(d
B)
Freq(GHz)
Ws=6mm
Ws=5mm
Ws=7mm
3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0
-35
-30
-25
-20
-15
-10
-5
0
5
Re
turn
Lo
ss(d
B)
Freq(GHz)
Ls=18mm
Ls=19mm
39
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tthhee ss lloott bb uutt wwiitthh iinnccrreeaassee iinn lleennggtthh oo ff tthhee ss lloo tt tthhee bbaannddwwiidd tthh iiss ddeecc rreeaass iinngg.. FFoorr LLss==1199 mmmm wwee ggoott
mmaaxxiimmuumm bbaannddwwiiddtthh wwhhiicchh iiss rreepprreesseenntteedd bbyy ddoo tttteedd lliinnee.
..
Figure 4.5: Comparing the results obtained by varying Feed point position
As you can see in figure 4.5, the bandwidth is maximum at probe feed position (0, 6.7)
when compared to other feed positions which is represented by continuous line. The s-parameter
variation is studied at different feed positions.
Figure 4.6: Comparing the results obtained by varying Radius of the Probe feed.
3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0
-40
-35
-30
-25
-20
-15
-10
-5
0
5R
etu
rn lo
ss(d
B)
Freq(GHz)
Feed point position
(0,6.5)
(0,6.7)
(0,6.9)
3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0
-40
-35
-30
-25
-20
-15
-10
-5
0
5
Ret
urn
loss
(dB
)
Freq(GHz)
R=0.6127
R=0.7127
R=0.7427
40
As you can see in figure 4.6, the resonant frequency is increasing with increase in radius
of probe feed but bandwidth is decreasing. After studying variation of s-parameter by varying the
radius of probe feed the maximum bandwidth is obtained when radius of probe feed as
0.7127mm which is represented by continuous line.
Best results were obtained for the following values of Ws, Ls, R and probe feed position.
Ls (length of the slot) = 19mm
Ws (width of the slot) = 6mm
R (radius of probe feed) = 0.7127mm
Probe feed position = (0, 6.7)
4.3.2 Return loss and VSWR display
Figure 4.7: Simulated Return Loss curve Figure 4.8: Simulated VSW R Curve
The simulated return loss is below −10 dB from 4.45 GHz to 7.4 GHz except at 5.1GHz.
The antenna is thin and compact which makes it easily portable.
41
4.3.3 Z-Parameter Display and Antenna Gain
Figure 4.9: Simulated Z-parameter
Figure 4.10: Gain Vs Frequency
A maximum gain of 8.77dB achieved at 4.7 GHz frequency. The Z-parameter was also
within the acceptable range.
42
4.3.4 Radiation Pattern
E plane(x-z) H plane(y-z)
Figure 4.11: E and H plane Radiation Pattern
Good broadside radiation patterns are observed. However, relatively large cross-
polarization radiation in the H-plane pattern is also seen, which is a common characteristic of
this kind of probe-fed microstrip antenna with a thick air substrate. The drop in broad side gain
at 6.5 GHz appears as a dip in the cross polarization patterns figure 4.10, which is due to the
increase in cross polarization levels.
43
CHAPTER 5
CONCLUSION AND FUTURE PROSPECTS
We have designed three different wideband microstrip patch antennas. The characteristics
of proposed antennas have been investigated through different parametric studies using IE3D
simulation software. The proposed antennas have achieved good impedance matching, stable
radiation patterns, and high gain. The phi-shaped antenna can be used for Wireless LAN
application in the frequency range 5.2 to 5.8 GHz. Fabrication and Verification of simulated
results can be carried out in future.
44
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